TRANSHEMISPHERIC PASSAGE OF MICROEMBOLI IN PATIENTS WITH UNILATERAL INTERNAL CAROTID-ARTERY OCCLUSION

Background and Purpose: Ischemic episodes distal to an internal caroti d artery occlusion are common. We undertook this study to look for evi dence of transhemispheric passage of embolic material in this patient category as a mechanism for embolic events. Methods: Seven symptomatic patients with unilateral internal carotid artery occlusion and contra lateral stenosis were examined by transcranial Doppler ultrasonography with 2-MHz probe (average monitoring time, 2.5 hours per patient). Bo th middle cerebral arteries and (if present) the reverse-flow anterior cerebral artery ipsilateral to the occluded internal carotid were mon itored. Three patients were reexamined 1 month after carotid endartere ctomy. Results: Embolic signals were detected in the middle cerebral a rtery ipsilateral to the stenosed internal carotid artery in all seven patients and in the opposite middle cerebral artery in four patients. In these four patients, a reverse-flow anterior cerebral artery was o bserved in which embolic signals were detected. No embolic signals wer e detected after surgery in any of the three patients who underwent ca rotid endarterectomy. Conclusions: Transhemispheric passage of embolic material occurs in patients with unilateral internal carotid artery o cclusion and contralateral stenosis. Endarterectomy of the stenosed in ternal carotid artery may eliminate the detected embolic signals in bo th hemispheres. Transcranial Doppler ultrasonography could be used as a diagnostic tool to identify the embolic source in patients with unil ateral carotid occlusion.